The present invention relates to a process for preparing novel, monodisperse crosslinked bead polymers having thiourea groups, and to their use for adsorbing metal compounds, in particular heavy metal compounds or noble metal compounds.
U.S. Pat. No. 4,444,961 discloses a process for preparing monodisperse, macroporous chelate resins. In this process, haloalkylated polymers are aminated and the aminated polymer is reacted with chloroacetic acid to give chelate resins of the iminodiacetic acid type.
The subject of the present invention is previously unknown monodisperse bead polymers, in particular monodisperse chelate resins functionalized with thiourea groups, a process for their preparation, and also their use.
Surprisingly, the monodisperse chelate resins having thiourea groups have a markedly higher adsorption capacity for metal compounds, in particular compounds of heavy metals or noble metals, than do the monodisperse, macroporous chelate resins disclosed in U.S. Pat. No. 4,444,961. A result of this is an improvement in the leakage behavior within the resin, reducing the amounts of metal residues in the eluate. The improved adsorption capability for heavy metal compounds and noble metal compounds is particularly apparent with elements of the platinum group, with bivalent ions from aqueous salt solutions or acids, in particular with noble metals such as rhodium, gold or silver, or noble-metal-containing catalyst residues.
However, the novel chelate resins can do more than merely purify aqueous salt solutions and acids with respect to metal residues. The novel chelate resins are also used in organic solvents or solutions of liquid or gaseous hydrocarbons or halogenated hydrocarbons, in particular chlorinated or fluorinated hydrocarbons.
To remove metal ions from liquid solutions, use is made industrially of ion exchangers that selectively adsorb these ions and are known as selective resins.
The treatment of process streams and waste water, specifically from the electroplating and surface finishing industry but also from the chemical and electronics industries, continues to increase in significance. It is an important precondition for the continued existence of numerous plants.
A central issue in the treatment of these aqueous or organic waste liquids, as well as in the treatment of landfill run-off and groundwater, is very extensive removal of metal ions, in particular heavy metal ions, such as those of mercury, iron, copper, nickel, and arsenic, or at least their removal down to very low residual concentrations.
Wet flue gas scrubbing in waste incineration plants or coal-fired power stations produces salt-rich waste water that contain considerable quantities of heavy metal ions. Modern incineration plants operate with two-stage scrubbing for separate adsorption of hydrochloric acid at pH&lt;1 and SO.sub.2 in the alkaline region. See C. Vater, J. An, and M. Jekel, Wasser, Abwasser 132, 565-571 (1991).
Acid scrubbers produce solutions containing hydrochloric acid, that are contaminated by a number of heavy metals. The hydrochloric acid solution from the scrubber contains mercury ions. Since in many cases it is desirable to obtain hydrochloric acid from the flue gas scrubber effluent, mercury must be very substantially removed therefrom. The macroporous, heterodisperse bead polymers used hitherto for this and having thiourea groups, disclosed in DE-A 2,429,944, have insufficient capability for the task. There is therefore a need for novel polymers with improved properties. In such cases the novel polymers functionalized with thiourea groups have an excellent purification action.
EP-A 422,480 describes a process for partial removal of trace elements from hydrocarbon mixtures using heterodisperse bead polymers having thiourea groups.
However, it is also known that heavy metals and their compounds occur not only in aqueous systems but also in the natural environment in many organic liquids and gases. For example, natural gases and natural gas condensates, mineral oils, and liquid or gaseous hydrocarbons in general, if they come from fossil sources, contain heavy metals and their compounds, for example, mercury, iron, nickel, phosphorus, arsenic, and others.
The petrochemical industry uses a large number of different process stages for the further processing of mineral oils and natural gases from various points of origin.
These stages include, inter alia, distillation steps, steam cracking or catalytic cracking and hydrogenation.
Use is frequently made in these processes of catalysts based on noble metals, inter alia platinum, palladium, and rhodium.
The action of these catalysts is to a considerable extent dependent on the absence of other metal or heavy metal compounds, for example, arsenic or mercury compounds. The presence of these substances can dramatically impair the action of the catalysts and poison the same. The term catalyst poisons is used.
Mercury is a corrosive metal that generally has a corroding action in pipelines and equipment due to amalgam formation and can bring about considerable corrosion damage.
There is therefore also a need to remove metal and/or heavy metal compounds from hydrocarbon mixtures. The macroporous, heterodisperse bead polymers used hitherto for this purpose and containing thiourea groups do not have sufficient capability for the task. The novel monodisperse polymers containing thiourea groups show markedly improved properties in this respect.
For recycling mercury from the waste water from alkali metal chloride electrolysis and purifying this waste water, use is made of combinations of anion exchangers and macroporous, heterodisperse bead polymers containing thiourea groups. According to DE-A 2,249,472, the latter polymer is used for ultrapurification.
For this application, too, the novel monodisperse polymers containing thiourea groups have improved properties. These markedly reduce heavy metals and their compounds not only in aqueous solutions but also, as described above, in organic liquids and vapors.